Anti-pollution ventilation system for spray-type coating chambers

ABSTRACT

An anti-pollution ventilation system includes means for circulating a fluid in a closed-loop path outside of a spray-type coating chamber. The circulating fluid is directed so as to form a fluid curtain across entrance and exit openings of the coating chamber. The system also includes a separator for continuously separating coating material from the circulating fluid. The separator comprises a plurality of side-by-side bores, having helical baffles therein, through which circulating fluid is directed. In one embodiment of the invention, some of the bores can be selectively closed. Means are included for transporting separated coating material from the separator back to the coating chamber for reuse. One refinement of the invention is to provide a bleeding means for bleeding fluid from the ventilation system, and another refinement is to provide a leakage collecting means for collecting leakage from the fluid curtains; in both cases a vapor-contaminant cleaner is provided to clean drained or leaked fluid before it is released to outside atmosphere. The ventilation system of this invention is further disclosed in combination with an irradiation type coating device wherein a coating chamber and an irradiating oven are located so close to one another that their inner atmospheres can mix. The inner atmospheres comprise mainly inert gases. In this embodiment, inert gas is bled from the ventilation system and fed to the irradiation oven.

United States Patent [191 Repp et al.

n] 3,750,622 [4 1 Au -mars ANTI-POLLUTION VENTILATION SYSTEM FOR SPRAY-TYPE COATING CHAMBERS [76] Inventors: Allen B. Repp, 24842 Penn Ave.,

Deal-born, Mich. 48124; William B. Berk, ,Ir., 22886 Evergreen Rd., Southfield, Mich. 48075 [22] Filed: June 11, 1971 [21] Appl. No.: 152,218

[52] 11.8. Cl 118/326, 55/237, 55/385, 55/D1G. 29, 55/467, 98/36, 98/115 SB, 261/79 A [51] Int. Cl. B05c 11/16 [58] Field of Search 98/115, 36, 115 SB; 55/235-239, 385, DIG. 29, 92; 261/79 A {56] References Cited UNITED STATES PATENTS Rl8,645 1111932 Whitmore 98/115 SB 582,892 5/1897 Abbott 55/238 983,877 2/1911 Cummings... 98/36 1,520,267 12/1924 Waltz 98/115 SB 1,970,077 8/1934 Collins 55/344 2,014,962 9/1935 Bramsen... 98/115 SB 2,057,579 10/1936 Kurth.... 55/228 2,216,390 10/1940 l-lawley 55/344 2,487,176 11/1949. Pitt et al.. 55/238 2,827,266 3/1958 RulT 98/36 2,074,317 3/1937 Allan et al. 55/DlG. 29

3,147,135 9/1964 Brown 118/326 3,270,711 9/1966 Leach 118/326 Primary Examiner-Hemard Nozick AttorneyGriffln, Branigan and Kindness [57] I ABSTRACT An anti-pollution ventilation system includes means for circulating a fluid in a closed-loop path outside of a spray-type coating chamber. The circulating fluid is directed so as to form a fluid curtain across entrance and exit openings of the coating chamber. The system also includes a separator for continuously separating coating material from the circulating fluid. The separator comprises a plurality of side-by-side bores, having helical baffles therein, through which circulating fluid is directed. In one embodiment of the invention, some of the bores can be selectively closed. Means are included for transporting separated coating material from the separator back to the coating chamber for reuse. One refinement of the invention is to provide a bleeding means for bleeding fluid from the ventilation system, and another refinement is to provide a leakage collecting means for collecting leakage from the fluid curtains; in both cases a vapor-contaminant cleaner is provided to clean drained or leaked fluid before it is released to outside atmosphere. The ventilation system of this invention is further disclosed in combination with an irradiation type coating device wherein a coating chamber and an irradiating oven are located so close to one another that their inner atmospheres can mix. The inner atmospheres comprise mainly inert gases. In this embodiment, inert gas is bled from the ventilation system and fed to the irradiation oven.

13 Claims, 8 Drawing Figures PATENIED 3. 750.622

sum 1 0F 3 ALLEN B. REPP WILLIAM E. BERK BY m ATTORNEYS ANTI-POLLUTION VENTILATION SYSTEM FOR SPRAY-TYPE COATING CHAMBERS BACKGROUND OF THE INVENTION This invention is related generally to the art of spraytype coating chambers and more particularly to ventilation systems for such coating chambers.

Spray-type coating chambers, or hoods, are widely used in manufacturing plants, such as in auto plants for painting articles with liquid and powdered paints or coating them with oil. Such chambers normally have entrance and exit openings through which conveyed articles pass. When spray-type coating chambers are used, however, pollution problems often arise. That is, coating-material contaminants escape from the chambers and contaminate surrounding atmospheres, thereby creating unfavorable working conditions in such manufacturing plants.

One prior art solution to this contamination problem is to employ a vacuum ventilation system for continually sucking excess sprayed coating material from a coating chamber and expelling it into outside atmosphere. Such a ventilation system usually sucks large amounts of air into the coating chamber so as to dilute the coating material which is expelled. Although this method cuts down on indoor air pollution it increases outdoor air pollution. Further this method is somewhat wasteful in that large amounts of coating material are thrown away. In addition, this method creates excessive air currents through the coating chamber which may cause undesirable concentrations of spray coating material if counter measures are not taken. Therefore, it

is an object of this invention to provide an antipollution ventilation system for spray-type coating chambers which does not excessively increase outdoor pollution, is not unduly wasteful, and does not create excessive air currents through a coating chamber.

Some prior art ventilation systems function substantially the same as those described in the previous paragraph, however, they further include separating means for recovering coating material and cleaning vapor contaminants from the air/coating-material mixture before it is blown into the outside atmosphere. Such systems suffer in that separators and contaminant cleaners are usually not efficient for low concentrations of atomized materials; therefore, by mixing large amounts of air, which are sucked into such prior art chambers, with coating material and contaminants, the separators and contaminant cleaners are caused to operate under relatively inefficient conditions. Thus, substantial amounts of coating material and vapor contaminants are still expelled into the outside atmosphere. Therefore, it is another object of this invention to provide an anti-pollution ventilation system for spray-type coating chambers in which separating elements and contaminant cleaners operate under efficient, highconcentration conditions.

At least one prior art ventilation system attacks the pollution problem by providing a closed loop-vacuum system (See US Pat. No. 2,848,353 to Norris). In this system, air is continuously sucked out of the coating chamber, cleaned and recirculated through spray guns. This system has two drawbacks. Firstly, it requires a modified liquid seal air-type compressor which is somewhat expensive. Secondly, this system causes excessive air currents through the coating chamber which is generally undesirable as pointed out above. Thus, it is yet another object of this invention to provide an antipollution ventilation system which does not require ex,-.

pensive equipment. 7

Turning now to still a third problem that exists in the prior art, as was pointed out above, some coating chambers have ventilation systems which include separators for separating coating material from air. In particular, some such separators comprise bores having helical baffles inserted therein through which an airparticulate mixture is directed. The efficiency of such separators depends to some extent on the velocity at which the mixture passes through the separators. Most prior art separators suffer because the velocity at which the mixture passes through the helical baffles cannot be controlled. Further, many prior art separators are not as efficient as they could be because they are not also combined with scrubbers. Therefore, it is still another object of this invention to provide a helical baffle separator in which the velocity at which fluid passes therethrough can be controlled and which can be selectively combined with a scrubber for increased efficiency.

SUMMARY OF THE INVENTION According to the principles of this invention, a fluid such as air, is circulated in a closed-loop path outside of a coating chamber. The circulating fluid is directed so as to form a fluid curtain across entrance and exit openings of the coating chamber. The air curtain picks up drainage passing out of the openings. Because there is very little outside air added to the circulating fluid, coating material and contaminants are at a high concentration level in the circulating fluid and can therefore be efficiently separated or cleaned out of the circulating fluid.

A separator continually cleans the circulating air. The separator comprises side-by-side bores having helically shaped baffles therein. There are cavities located above and below the baffles. In one embodiment a liquid is sprayed on the baffles. In another embodiment the bores can be selectively closed off. Separated coating material is transported back to the coating chamber for reuse.

In one refinement of the invention a bleeding means is provided to bleed fluid from the circulating fluid and in another refinement a leakage collecting means is provided to collect leakage from the circulating fluid; in both refinements a vapor contaminant cleaner is provided to clean fluid before it is released into outside atmosphere.

The ventilation system of this invention makes it possible to use a coating chamber in close physical association with an irradiation oven; and a preferred embodiment of this combination is disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention in a clear manner.

FIG. 1 is an exploded isometric view of a spray-type coating chamber and a ventilation system employing principles of this invention;

FIG. 2 is a detailed cross-sectional view of that portion of the ventilation system of FIG. 1 which creates an air curtain in front of a spray-chamber entrance door;

FIG. 3 is a partially cutaway rear view of the separator shown in FIG. l;

FIG. 4 is'a simplified sectional view taken along line 44 in FIG. 3.

FIG. 5 is a cross-sectional view taken on line 5-5 in FIG. 3;

FIG. 6 is a close-up view of a tube and helically shaped baffle'which is used in the separator of FIG. 3;

FIG. 7 is a simplified sectional view similar to FIG. 3, but also showing a liquid disperser;

FIG. 8 is an isometric view of a spray-type chamber having a closed-loop ventilation system and used in combination with an irradiating oven.

DESCRIPTION OF THE PREFERRED EMBODIMENT.

Referring now to FIG. 1 there is shown a spray-type coating chamber 10, a coating system 11, a closed loop ventilation system 12 and a conveyor system 13. The coating chamber is metallic and has vertical walls 14, sloping door panels 16, a sloping bottom pan 18, an

entrance vestibule (See also FIG. 2) and an exit ves-- tibule 22. The sloping door panels 16 are spaced apart from one another at their top edges so as to form a slot 24 which is closed by a flexible seal 26 (shown pulled open in the drawing). The entrance and exit vesibules 20 and 22 also have slots 28 in the tops thereof in line with slot 24 which are also covered with flexible seals (not shown in FIG. 1). Further, the entrance and exit vestibules 20, 22 have entrance and exit openings or doors however, only the entrance door 30 can be seen in FIGS. 1 and 2.

The coating system 11 includes coating elements 34, a driving mechanism 36 and a coating-material reservoir 38.

In the preferred embodiment, the coating elements 34 are spray-guns and the driving mechanism 36 is a compressor, however, the coating elements could also be mechanical turbulent elements as well as other types of coating material dispersing elements. The driving mechanism 36 is interconnected with each of the coating elements 34 by appropriate driving lines 40. The driving mechanism 36 is in turn coupled to the coatingmaterial reservoir 38. The coating material reservoir 38 receives recaptured coating material through. a separator recapture line 42 and a primary-recapture line 43.

The conveyor system 13 comprises a track 44 and hooks and rollers 46 which move along the track 44. In FIG. 1 hub caps 48 are shown attached to the hooks and rollers 46.

The closed loop ventilation system 12 comprises a duct work which includes a separator 50, a front duct 54 having left and right legs 56 and 58, and left and right back ducts 60 and 62. A motor-driven fan 52 is located in the front duct 54 and drives fluid in the front duct 54 toward the left and right legs 56 and S8. The front duct 54 is connected to the bottom portion of the separator 50 and its left leg 56 has an opening 57 (shown in FIG. 2) at a side of the entrance door 30. The left back duct 60 extends from the top portion of the separator 50 downwardly to an opening 59 on a side of the entrance door 30 opposite from the opening 57 inthe left leg 56 of the front duct 54. The opening 59 and the opening 57 define an entrance gap 61 through which fluid exiting from the entrance opening 30 passes. The right back duct 62 is also attached to the separator 50 at an upper portion thereof and extends downwardly to open at a side of the exit door (not shown) opposite a opening (not shown) in the right leg 58 of the front duct 54. Again an exit gap is defined through which fluid exiting from the exit opening (not shown) must pass. Across this exit gap, as well as the entrance gap 61 (See FIG. 2) air is blown, as shown by arrows in FIG. 2, thereby creating air curtains. Slidable baffles 64 are mounted at the openings of the right and left legs of the front ducts and the left and right back ducts (See FIG. 2). These baffles can be selectively slid across their respective openings so as to increase or decrease the size of the openings.

An additional refinement of the FIG. 1 embodiment further includes a bleed-off duct 80 connected to the front duct 54. The bleed-off duct 80 leads from the front duct 54 to a solvent cleaner 82 which, in turn, exhausts to outside atmosphere through an exhaust duct 83. In a' preferred embodiment the solvent cleaner 82 comprises a heating element (not shown); however, a cooling element could also be used in the solvent cleaner 82. A shiftable baffle 84 is mounted inside the front duct 54 adjacent to the attachment area of the bleed-off duct 80. By shifting the shiftable baffle 84 the amount of fluid flowing to the bleed-off duct 80 can be controlled.

A further refinement of the FIG. 1 embodiment is the leakage funnels 86 located above the entrance and exit doors 30. The leakage funnels 86 are connected to the solvent cleaner 82 by leakage ducts 88.

The separator 50 can be more clearly seen in FIGS. 3-6. The separator 50 comprises an upper cavity 66 a lower cavity 68 and separating elements 70 (the separating elements are not shown in detail in FIG. 4).

The separating elements 70 include an impervious upper frame 72, a supporting lower frame 73, tubes 74 having bores and helically shaped baffles 76. The tubes'74 are supported side-by-side-by the impervious upper frame 72 and the supporting lower frame 73.

A separator baffle 71 (FIG. 4) is positioned immediately above the tubes 74 and can be slid so as to close off the bores 75 of some or all of the tubes 74.

FIG. 7 shows essentially the same separator shown in FIG. 3-6 with the further inclusion of a liquid dispensor 78 which can selectively be madeto spray a liquid from a nozzle 79 above the separating elements 70.

Turning next to the operation of the systems shown in FIG. 1-7, articles such as hub caps 48, conveyed by the conveyor system 13 are transported into the entrance door 30 of the coating chamber 10 and out the exit door. At the same time coating elements 34 atomize a coating material within the coating chamber 10. The coating elements 34 blow approximately 20 cubic feet of air each into the coating chamber 10, thus, a small amount of pressure is built up in the chamber. This pressure is relieved through the entrance and exit vestibules 20 and 22 and the entrance and exit doors. The flexible seal 26 prevents release of pressure through the slot 24. The pressure to be relieved is small and movement of air inside the coating chamber 10 is not significant; thus, after the coating elements 34 have been in operation for a short length of time a coating fog will develop within the chamber. However, relief of pressure through the vestibules 20 and 22 will cause some movement of air within the chamber through these vestibules.

The motor driven fan 52 causes closed-loop air circulation through the front duct 54, down through the left and right legs 56, 58 across the gap 61 (FIG. 2) and a similar gap (not shown) at the exit opening, through the left and right back ducts 60,62, into the upper cavity 66 of the separator 50, down through the separating elements 70 of the separator 50, into the lower cavity 68 of the separator 50, and back to the fan 52. Thus, the closed loop ventilation system creates curtains of air in front of the entrance opening 30 and exit opening (not shown). This curtain picks up air coming out of the coating chamber 10, as well as the atomized coating material and solvent vapors carried thereby, and adds them to the stream of air being circulated through the closed-loop system. As the circulating air passes through the separator SO, much of the atomized coating material is separated from the circulating air and returned via the recapture line 42 to the coating material reservoir 38. However, that atomized coating material which is not separated by the separator 50 on its first revolution will be recirculated and separated on a later revolution. Eventually, the concentration of atomized coating material in the circulating air reaches such a level that the separator 50 functions relatively efficiently and separates out essentially the same amount of atomized coating material as is added for each cycle.

As air is added to the coating chamber by the coating elements 34 some air must drain out of the system. In this regard, if no action is taken excess air will leak out of the system at the air curtain gaps. Experiments conducted to date have shown that this leaking results in very little pollution. It appears that most of the leaked air is that which exits from the left and right legs 56, 58 and such air has already passed through the separator 50. However, pollution can be further reduced by employing either the bleed-off system or the leakage system shown in FIG. 1.

With regard to the bleed-off system, the shiftable baffle 84 is set to bleed-off a predetermined amount of air into the bleed-off duct 80. The bled off air contains contaminants in the form of solvent vapors. These vapors are reduced from the air by the solvent cleaner 82 before being exhausted to the outside atmosphere. The amount of air which must be bled off is relatively small as it only includes that amount of air which is ejected into the coating chamber 10 by the coating elements 34. Thus, the concentration of solvent vapors in the bled-off air is relatively large and the solvent cleaner 82 can therefore operate at an efficient, high level vapor concentration.

The leakage system of FIG. 1 functions somewhat similarly as does the bleed-off system of FIG. 1 in that leakage from the air curtain gaps rises into the leakage funnels 86 and thereafter passes through the solvent cleaner 82 into the outside atmosphere.

Operation of the separator 50 is as follows: referring to FIGS. 3-6, air, laden with coating material, passes into the upper cavity 66 of the separator and is forced downwardly through the helically shaped baffles 76. While traveling through the helically shaped baffles the air is caused to travel in a circular path. This creates a centrifugal force, which throws atomized particles outwardly against the sides of the bores 74. When pressed together against the bore s sides the particles coalesce and flow downwardly into the lower cavity 68 and the separator recapture line 42.

To increase the velocity at which air travels around the helically shaped baffles 76 the separator baffle 77 is moved to cover more or less of the bores 74 so that air has more or fewer bores through which to go. This means of regulation can also be used to clean certain ones of the helically shaped baffles 76 by concentrating flows of air through those baffles to be cleaned.

To increase the efficiency of the separator 50 the liquid dispenser 78 shown in FIG. 7 can be employed. This dispenser dispenses a liquid, such as the coating material, above the separating elements so as to act as a scrubber; thereby aiding in separating atomized coating material from air.

Returning to the operation of the overall system shown in FIG. 1, by moving the slidable baffles 64 to open or close the duct openings 57 and 54 (FIGS. 1 and 2) the velocity at which such air flows across the gap 61 can be regulated. In this regard, higher velocities appear to pick up material flowing out of the coating chamber 10 more efficiently, however, lower velocities must be used for some articles which are easily blown.

It will be understood by those skilled in the art that this invention provides a coating chamber ventilation system which not only prevents pollution but also contributes to an extremely efficient coating system. For example, because there is very little air movement in the coating chamber 10 a fog of coating material can be built up within the chamber. Further, this system provides economic benefits in that excessive coating material is not exhausted but rather reused. In addition, the separator 50 and solvent cleaner 82 are able to operate under efficient, high concentration conditions.

Turning next to the combination device of FIG. 8, there is shown the coating chamber 10 and the ventilation system 12 in combination with an irradiation oven 90. The ventilation system of FIG. 8 differs only from the ventilation system of FIG. 1 in that the solvent cleaners exhaust duct 83 exhausts into the irradiation oven rather than into outside atmosphere.

In operation, nitrogen is used to drive the coating elements 34. Eventually, the coating chamber 10 fills with nitrogen and nitrogen therefore passes out through the chambers entrance and exit openings. This nitrogen is picked up into the closed loop ventilation system 12 by curtains of air as was previously described. As the closed loop ventilation system 12 is bled through the bleed off duct 80, as was previously described, the irradiation oven is also filled with nitrogen from the exhaust duct 83. Because the coating system and the irradiation system are filled with nitrogen they can be in close physical proximity, one to the other, as is shown in FIG. 8.

One skilled in the art will readily recognize the merits of this system. Not only can the coating chamber be positioned close to the irradiating oven but the nitrogen is fed to the whole system through only the coating ele ments 34. The remainder of the required nitrogen circulation follows automatically.

It can be appreciated by those skilled in the art that the ventilation system that is herein disclosed has many benefits over prior art ventilation systems. While the invention has been particularly shown and described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention. For example, additional separating or scrubbing means can be added to the closed loop ventilation system. Further, the bleed-off duct 80 can be connected to the closed loop ventilation system at points other than that shown in FIG. 1. In addition, a solvent cleaner such as solvent cleaner 82 could be added directly to the closed loop ventilation system. Although the ventilation system of this invention has been described in a coating-chamber environment it should be understood that it can be used in other environments wherein there are chambers having polluted atmospheres therein. Further, it should be understood that when the ventilation system of this invention is used in a coating chamber environment it is effective for most types of coating materials, including liquids and powders.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

l. A spray-type coating system comprising:

a coating chamber of the type having a coating chamber opening through which work pieces can pass into said coating chamber along a work-piece path;

a spraying device located in said chamber for receiving coating material and spraying said coating material in atomized form in said coating chamber, thereby establishing an atomized coating-material environment inside said chamber; coating-material reservoir in communication with said spraying device for continually feeding coating material to said spraying device; ventilation system including, a motivating means for circulating gas and a duck-work means for guiding said circulating gas along an endless, closed, gas-flow path, said duct-work means defining a first port on one side of said coating-chamber opening and a second port on the other side of said coatingchamber opening, thereby establishing a duct-work gap across said coating-chamber opening, wherein said motivating means causes said circulating gas in said endless, closed, gas-flow path to travel out of said first port, across said coating-chamber opening in a substantially straight path, and into said second port to thereby produce a flowing gas curtain across said work-piece path through said opening, said ventilation system further including a separating means located in said duct-work system for separating coating material from said circulating gas; and a recapture means connected between said separating means and said coating-material reservoir for recapturing said separated coating material and 8 transferring said recaptured coating material to said coating-material reservoir;

whereby said circulating gas in said endless closed gas-flow path is continually cleaned by said separating means, and said coating material which is thereby recaptured is returned to said coatingmaterial reservoir for reuse.

2. A ventilation system as claimed in claim 1 wherein said separating means includes a helically shaped baffle.

3. A ventilation system as claimed in claim 1 wherein said separating means includes:

an impervious frame supporting parallel tubes having bores therein; and,

a helically shaped baffle in the bore of each of said tubes.

4. A ventilation system as claimed in claim 3 and fur' ther including a closing means for selectively closing some of said bores.

S. A ventilation system as claimed in claim 3 wherein said separating means further includes a liquid dispensing means for dispensing liquid on said tubes.

6. A ventilation system as claimed in claim 1 wherein is further included a bleeding system for bleeding a portion of said gas from said circulating gas in said endless, closed, gas-flow path.

7. A ventilation system as claimed in claim 6 wherein said bleeding system includes an adjustable means for adjusting the amount of gas bled from said endless, closed, gas-flow path.

8. A ventilation system as claimed in claim 7 wherein said bleeding system includes a contaminant cleaner for cleaning vapors from the bled-off gas.

9. .A ventilation system as claimed in claim 6 wherein said bleeding system is connected downstream of said separating means and upstream of said gas curtain.

10. A ventilation system as claimed in claim 1 wherein is further included a leakage collecting system located in close proximity to said gas curtain for collecting leakage from said gas curtain.

11. A ventilation system as claimed in claim 10 wherein said leakage collecting system further includes a vapor-contaminant cleaner for cleaning contaminating vapors from said collected leakage.

12. A ventilation system as claimed in claim 10 wherein said leakage collecting system comprises a funnel positioned above said gas curtain.

13. A ventilation system as claimed in claim 12 wherein said leakage collecting system further includes a vapor contaminant cleaner for cleaning vapors from 

1. A spray-type coating system comprising: a coating chamber of the type having a coating chamber opening through which work pieces can pass into said coating chamber along a work-piece path; a spraying device located in said chamber for receiving coating material and spraying said coating material in atomized form in said coating chamber, thereby establishing an atomized coatingmaterial environment inside said chamber; a coating-material reservoir in communication with said spraying device for continually feeding coating material to said spraying device; a ventilation system including, a motivating means for circulating gas and a duck-work means for guiding said circulating gas along an endless, closed, gas-flow path, said duct-work means defining a first port on one side of said coating-chamber opening and a second port on the other side of said coating-chamber opening, thereby establishing a duct-work gap across said coating-chamber opening, wherein said motivating means causes said circulating gas in said endless, closed, gas-flow path to travel out of said first port, across said coating-chamber opening in a substantially straight path, and into said second port to thereby produce a flowing gas curtain across said work-piece path through said opening, said ventilation system further including a separating means located in said duct-work system for separating coating material from said circulating gas; and a recapture means connected between said separating means and said coating-material reservoir for recapturing said separated coating material and transferring said recaptured coating material to said coating-material reservoir; whereby said circulating gas in said endless closed gas-flow path is continually cleaned by said separating means, and said coating material which is thereby recaptured is returned to said coating-material reservoir for reuse.
 2. A ventilation system as claimed in claim 1 wherein said separating means includes a helically shaped baffle.
 3. A ventilation system as claimed in claim 1 wherein said separating means includes: an impervious frame supporting parallel tubes having bores therein; and, a helically shaped baffle in the bore of each of said tubes.
 4. A ventilation system as claimed in claim 3 and further including a closing means for selectively closing some of said bores.
 5. A ventilation system as claimed in claim 3 wherein said separating means further includes a liquid dispensing means for dispensing liquid on said tubes.
 6. A ventilation system as claimed in claim 1 wherein is further included a bleeding system for bleeding a portion of said gas from said circulating gas in said endless, closed, gas-flow path.
 7. A ventilation system as claimed in claim 6 wherein said bleeding system includes an adjustable means for adjusting the amount of gas bled from said endless, closed, gas-flow path.
 8. A ventilation system as claimed in claim 7 wherein said bleeding system includes a contaminant cleaner for cleaning vapors from the bled-off gas.
 9. A ventilation system as claimed in claim 6 wherein said bleeding system is connected downstream of said separating means and upstream of said gas curtain.
 10. A ventilation system as claimed in claim 1 wherein is further included a leakage collecting system located in close proximity to said gas curtain for collecting leakage from said gas curtain.
 11. A ventilation system as claimed in claim 10 wherein said leakage collecting system further includes a vapor-contaminant cleaner for cleaning contaminating vapors from said collected leakage.
 12. A ventilation system as claimed in claim 10 wherein said leakage collecting system comprises a funnel positioned above said gas curtain.
 13. A ventilation system as claimed in claim 12 wherein said leakage collecting system further includes a vapor contaminant cleaner for cleaning vapors from leakage collected. 